1. Field of the Invention
The present invention relates to a brushless electric motor, more particularly to an electric control apparatus in combination with a torque command signal generator for controlling an output torque of the brushless electric motor in accordance with a torque command signal from the signal generator.
2. Description of the Prior Art
In Japanese Patent Laid-open Publication No. 64-64583, there is disclosed an electric control apparatus which includes an encoder for detecting a rotational speed of the rotor of a motor. In the control apparatus, an address signal is formed in accordance with the rotational speed of the rotor, and a sine wave signal is read out from a sine-wave memory at a frequency proportional to the rotor speed. The amplitude of the sine wave signal is linearly controlled, in response to a torque command signal from an associated signal generator, to apply a motor current to the stator windings of the motor for controlling the rotation of the motor. In general, the encoder is composed of light emitting and receiving elements opposed to one another through a rotary disc with a slit, a driving circuit for activating the light emitting element, and a receiving circuit for receiving a signal detected by the light receiving element. The driving circuit and the receiving circuit, however, become unstable when operating under high temperature conditions. For this reason, the conventional electric control apparatus for the brushless electric motor may not be used in a high temperature enviroment.